Sorel cement is a term used to refer to various compositions having as basic ingredients a combination of magnesia (MgO) and magnesium chloride (MgCl.sub.2) in an aqueous solution. This basic Sorel formula system when cured is a magnesium oxychloride hydrate.
Sorel cement was discovered almost 100 years ago. It gets harder, and sets faster than Portland cement, but its widespread use has been greatly limited because of its inherent poor water resistance. The magnesium oxychloride hydrate crystals that compose the Sorel cement have been found to have a structure very much like gypsum in that the physical properties of the cement depend on an intimate infiltration of the crystals, one with another, but with no real bond between the crystals. The Sorel cement product is also somewhat soluble in water with the result that exposure to water virtually eliminates the adhesion between the crystals.
Various attempts have been made to overcome this difficulty such as the addition of materials which have the property of forming insoluble magnesium salts, such as phosphates and aluminates. The results have been only partially successful and in fact usually with the further disadvantage that the hardening rate is greatly slowed.
Various fillers have been reported in the literature, but mainly from the point of view of their compatibility rather than that they impart any special properties to the cement. Glass fibers have been tried with some success, but the bond between the glass fibers and the Sorel cement is destroyed by exposure to water and thus the structural advantages of the glass fibers are only temporary.
It is obvious from repeated statements in the literature that had it not been for the water sensitivity of Sorel cement products, their use would have been much more general and wide spread. It is exactly because of this drawback of these cement products that there remains a large potential for these materials if the water sensitivity problem could be solved. The superior hardening rate, greater strength and excellent fire retardant properties of Sorel cement could then be taken advantage of in a host of building materials where its use is presently not considered.